In all seriousness, though, I don't keep up with political movements as much as I should. The best thing I can think of is Feinstein's firearm stances and the groups that support her propositions, and I only think it's crazy because people don't actually do any research before they throw in their support.

I don't think you are going to find many extremist groups that liberals would identify as left-wing extremists. The terms right-wing and left-wing are nebulous enough phrases that accentuating one or another aspect of an ideology allows that ideology to be identified as either right-wing or left-wing as desired. Go too far to the left and the left simply redefines you as a right-wing extremist. This is how the former heads of Communist and Socialist parties get classified as right-wing extremists despite the fact that Socialism and Communism are generally accepted as left-wing ideologies. (Ask reddit if Stalinists and Maoists and Neo-Nazis are left-wing extremists - and if Stalin and Mao and Hitler were left-wing extremists.)